text: import collections
  import itertools
  import logging
  
  import pykka
  
  import mopidy
  from mopidy import audio, backend, mixer
  from mopidy.audio import PlaybackState
  from mopidy.core.history import HistoryController
  from mopidy.core.library import LibraryController
  from mopidy.core.listener import CoreListener
  from mopidy.core.mixer import MixerController
  from mopidy.core.playback import PlaybackController
  from mopidy.core.playlists import PlaylistsController
  from mopidy.core.tracklist import TracklistController
  from mopidy.internal import path, storage, validation, versioning
  from mopidy.internal.models import CoreState
  
  logger = logging.getLogger(__name__)
  
  
  class Core(
      pykka.ThreadingActor,
      audio.AudioListener,
      backend.BackendListener,
      mixer.MixerListener,
  ):
  
      library = None
      """An instance of :class:`~mopidy.core.LibraryController`"""
  
      history = None
      """An instance of :class:`~mopidy.core.HistoryController`"""
  
      mixer = None
      """An instance of :class:`~mopidy.core.MixerController`"""
  
      playback = None
      """An instance of :class:`~mopidy.core.PlaybackController`"""
  
      playlists = None
      """An instance of :class:`~mopidy.core.PlaylistsController`"""
  
      tracklist = None
      """An instance of :class:`~mopidy.core.TracklistController`"""
  
      def __init__(self, config=None, mixer=None, backends=None, audio=None):
          super().__init__()
  
          self._config = config
  
          self.backends = Backends(backends)
  
          self.library = pykka.traversable(
              LibraryController(backends=self.backends, core=self)
          )
          self.history = pykka.traversable(HistoryController())
          self.mixer = pykka.traversable(MixerController(mixer=mixer))
          self.playback = pykka.traversable(
              PlaybackController(audio=audio, backends=self.backends, core=self)
          )
          self.playlists = pykka.traversable(
              PlaylistsController(backends=self.backends, core=self)
          )
          self.tracklist = pykka.traversable(TracklistController(core=self))
  
          self.audio = audio
  
      def get_uri_schemes(self):
          """Get list of URI schemes we can handle"""
          futures = [b.uri_schemes for b in self.backends]
          results = pykka.get_all(futures)
          uri_schemes = itertools.chain(*results)
          return sorted(uri_schemes)
  
      def get_version(self):
          """Get version of the Mopidy core API"""
          return versioning.get_version()
  
      def reached_end_of_stream(self):
          self.playback._on_end_of_stream()
  
      def stream_changed(self, uri):
          self.playback._on_stream_changed(uri)
  
      def position_changed(self, position):
          self.playback._on_position_changed(position)
  
      def state_changed(self, old_state, new_state, target_state):
          # XXX: This is a temporary fix for issue #232 while we wait for a more
          # permanent solution with the implementation of issue #234. When the
          # Spotify play token is lost, the Spotify backend pauses audio
          # playback, but mopidy.core doesn't know this, so we need to update
          # mopidy.core's state to match the actual state in mopidy.audio. If we
          # don't do this, clients will think that we're still playing.
  
          # We ignore cases when target state is set as this is buffering
          # updates (at least for now) and we need to get #234 fixed...
          if (
              new_state == PlaybackState.PAUSED
              and not target_state
              and self.playback.get_state() != PlaybackState.PAUSED
          ):
              self.playback.set_state(new_state)
              self.playback._trigger_track_playback_paused()
  
      def playlists_loaded(self):
          # Forward event from backend to frontends
          CoreListener.send("playlists_loaded")
  
      def volume_changed(self, volume):
          # Forward event from mixer to frontends
          CoreListener.send("volume_changed", volume=volume)
  
      def mute_changed(self, mute):
          # Forward event from mixer to frontends
          CoreListener.send("mute_changed", mute=mute)
  
      def tags_changed(self, tags):
          if not self.audio or "title" not in tags:
              return
  
          tags = self.audio.get_current_tags().get()
          if not tags:
              return
  
          self.playback._stream_title = None
          # TODO: Do not emit stream title changes for plain tracks. We need a
          # better way to decide if something is a stream.
          if "title" in tags and tags["title"]:
              title = tags["title"][0]
              current_track = self.playback.get_current_track()
              if current_track is not None and current_track.name != title:
                  self.playback._stream_title = title
                  CoreListener.send("stream_title_changed", title=title)
  
      def _setup(self):
          """Do not call this function. It is for internal use at startup."""
          try:
              coverage = []
              if self._config and "restore_state" in self._config["core"]:
                  if self._config["core"]["restore_state"]:
                      coverage = [
                          "tracklist",
                          "mode",
                          "play-last",
                          "mixer",
                          "history",
                      ]
              if len(coverage):
                  self._load_state(coverage)
          except Exception as e:
              logger.warn("Restore state: Unexpected error: %s", str(e))
  
      def _teardown(self):
          """Do not call this function. It is for internal use at shutdown."""
          try:
              if self._config and "restore_state" in self._config["core"]:
                  if self._config["core"]["restore_state"]:
                      self._save_state()
          except Exception as e:
              logger.warn("Unexpected error while saving state: %s", str(e))
  
      def _get_data_dir(self):
          # get or create data director for core
          data_dir_path = (
              path.expand_path(self._config["core"]["data_dir"]) / "core"
          )
          path.get_or_create_dir(data_dir_path)
          return data_dir_path
  
      def _get_state_file(self):
          return self._get_data_dir() / "state.json.gz"
  
      def _save_state(self):
          """
          Save current state to disk.
          """
  
          state_file = self._get_state_file()
          logger.info("Saving state to %s", state_file)
  
          data = {}
          data["version"] = mopidy.__version__
          data["state"] = CoreState(
              tracklist=self.tracklist._save_state(),
              history=self.history._save_state(),
              playback=self.playback._save_state(),
              mixer=self.mixer._save_state(),
          )
          storage.dump(state_file, data)
          logger.debug("Saving state done")
  
      def _load_state(self, coverage):
          """
          Restore state from disk.
  
          Load state from disk and restore it. Parameter ``coverage``
          limits the amount of data to restore. Possible
          values for ``coverage`` (list of one or more of):
  
              - 'tracklist' fill the tracklist
              - 'mode' set tracklist properties (consume, random, repeat, single)
              - 'play-last' restore play state ('tracklist' also required)
              - 'mixer' set mixer volume and mute state
              - 'history' restore history
  
          :param coverage: amount of data to restore
          :type coverage: list of strings
          """
  
          state_file = self._get_state_file()
          logger.info("Loading state from %s", state_file)
  
          data = storage.load(state_file)
  
          try:
              # Try only once. If something goes wrong, the next start is clean.
              state_file.unlink()
          except OSError:
              logger.info("Failed to delete %s", state_file)
  
          if "state" in data:
              core_state = data["state"]
              validation.check_instance(core_state, CoreState)
              self.history._load_state(core_state.history, coverage)
              self.tracklist._load_state(core_state.tracklist, coverage)
              self.mixer._load_state(core_state.mixer, coverage)
              # playback after tracklist
              self.playback._load_state(core_state.playback, coverage)
          logger.debug("Loading state done")
  
  
  class Backends(list):
      def __init__(self, backends):
          super().__init__(backends)
  
          self.with_library = collections.OrderedDict()
          self.with_library_browse = collections.OrderedDict()
          self.with_playback = collections.OrderedDict()
          self.with_playlists = collections.OrderedDict()
  
          backends_by_scheme = {}
  
          def name(b):
              return b.actor_ref.actor_class.__name__
  
          for b in backends:
              try:
                  has_library = b.has_library().get()
                  has_library_browse = b.has_library_browse().get()
                  has_playback = b.has_playback().get()
                  has_playlists = b.has_playlists().get()
              except Exception:
                  self.remove(b)
                  logger.exception(
                      "Fetching backend info for %s failed",
                      b.actor_ref.actor_class.__name__,
                  )
  
              for scheme in b.uri_schemes.get():
                  assert scheme not in backends_by_scheme, (
                      f"Cannot add URI scheme {scheme!r} for {name(b)}, "
                      f"it is already handled by {name(backends_by_scheme[scheme])}"
                  )
                  backends_by_scheme[scheme] = b
  
                  if has_library:
                      self.with_library[scheme] = b
                  if has_library_browse:
                      self.with_library_browse[scheme] = b
                  if has_playback:
                      self.with_playback[scheme] = b
                  if has_playlists:
                      self.with_playlists[scheme] = b
  